Enhancement of gamma benzene hexachloride content



ENHANCEMENT OF GAME IA- BENZENE HEXACHLGRIDE CONTENT George Calingaert,Geneva, N. Y., assignor to Ethyl Corporation, New York, N. Y., acorporation of Delaware Original application December 24, i949, SerialNo. 135,022. Divided and this application May 5, 1953, Sen'al No.353,081

7 Claimst (Cl. 260-648)- This invention relates'to an integrated processfor making gamma benzene hexachloride and trichlorobenzene from chlorineand benzene. This application is a division of my co-pending applicationSerial No. 135,022, filed December 24, 1949; nowabandoned:

A mixture of isomerso'f benzene hexachloride including arelatively'small quantity of the" gamma isomer, has been used for anumber of years as an" insecticide. The mixture of isomers has certaindisadvantages not obtained'when the gamma isomerof benzene hexachlorideis used alone. Thus a substantially pure gamma isomer known as lindaneis becoming an important commercial insecticide. The other isomers ofbenzene hexachloride both have practically no potency as insecticidesand are objectionable from the standpoint of odor and other undesirableproperties. isomers have had very little value. However, by the processof my invention, the non-gamma isomers are cracked; either thermally orcatalytically, to a substantially pure trichlorobenzene, a valuableproduct since it is an outstanding scavenger for use in leaded gasoline,as disclosed in U. S. Patent 2,479,903. The purity of trichlorobenzeneis importantto its scavenging properties and although trichlorobenzenecan be made by the direct chlorination of benzene, undesirableby-products such as tetrachlorobenzene are produced which must beseparated and have practically nosal'va'ge value.

It is therefore an object of my invention to produce from benzene andchlorine a substantially pure gamma benzene hexachloride and asubstantially pure trichlorobenzene.

I accomplish this object by reacting chlorine and benzene preferably inthe presence of actinic light whereby a mixture of isomers of benzenehexachloride is formed. From such mixture the gamma isomer is separatedfrom the non-gamma isomers, the latter being then converted to asubstantially pure trichlorobenzene by cracking.

My invention can be best understood by referring to the drawing which isa schematic flow diagram illustrating the process of my invention.Chlorine is charged through line 10 and benzene through line 11 to thereactor 12. In the reactor 12 are daylight fluorescent lights whichphotochemically convert the chlorine and benzene to benzenehexachloride. The reactor 12 is maintained under substantiallyatmospheric pressure or under a pressure sufiicient to force thereaction products through the system. The temperature in the reactor ispreferably maintained between about 40 C. and 60 C.

The reaction products pass from the reactor 12 through line 13 to thecaustic scrubber 14 in which is removed traces of unreacted chlorine andany hydrogen chloride formed in the reactor. From the caustic scrubber14 the mixture of benzene hexachloride and unreacted benzene passthrough line 15 to the vaporizer 16. The vaporizer 16 is maintained atsuch a temperature that the unconverted benzene is removed overheadthrough line 17. Recycle benzene is blended with the incoming freshThus, the non-gamma ited States atent ice 2,773,103- Patented Dec. 4,1956 benzene through line 11 and recharged to the reactor 12. Thebenzene hexachloride containing the various isomers is removed from thebottom of vaporizer 16 through line 18, mixed with a solvent selectiveto the gamma isomer, andthe mixture charged through line 19 to the gammaextractor vessel 20, the solvent being charged through line 21. Thevessel 20 serves to give the gamma isomer time to go into solution andis maintained under substantially atmospheric pressure and at atemperature of between approximately 15 C. and 25 C.

While I preferably use a, solvent extraction method for separating thegamma isomer from the non-gamma isomers, other separation methods can beused within-the scope of my invention. Furthermore, while I prefer toseparate all the gamma from the non-gamma, it is not always advantageousto do so and therefore a certain amount of the gamma isomer may becharged along with the non-gamma isomer to the cracking stage. I preferto use as the solvent one of the lower alcohols such as methyl, ethyl orpropyl although other solvents may be used such as benzene,trichlorobenzene, lower alkyl acetates and lower alkyl ethers.

The solution of solvent and gamma isomer together with precipitatednon-gamma isomers and some undissolvcd gamma isomers are discharged fromthe extractor 20 through line 22 to a conventional filter 23. the filter23, the filtrate containing thegamma isomer. passes through line 24 tothe evaporator 25 maintained at a temperature of between and 100 C., inwhich the solvent is separated from the gamma isomer. The

gamma isomer leaves the evaporator 25 through line 26- throughlines 31and 32 to the gamma extractor 20. Also from the evaporator 25 solvent isremoved through line 33 and recycled to the gamma extractor 20.

The filter cake from the filter 23 containing a small portion of gammaisomer but in the main containing nongamma isomers is charged throughline 34 to the cracker 35 in which hydrogen chloride is split off fromthe henzene hexachloride leaving trichlorobenzene. The hydrogen chlorideis removed from the cracker 35 through line 3. The trichlorobenzenetogether with the unconverted benzene hexachloride and a relativelysmall portion of other chlorinated benzenes are discharged through line37 to the rectifying column 38. This column is maintained undersubstantially atmospheric pressure at a temperature corresponding to theboiling point of trichlorobenzene, namely about 210 C. Thetrichlorobenzene produced is removed from the system through line 39 andthe unconverted benzene hexachloride is recycled to the cracker 35through line 40.

The cracking step may be either thermal or catalytic. When no catalystis used, the temperature range is from about 500 to 600 C. If a catalystsuch as ferric chloride is used, the temperature of the cracking step ismaintained between 270 and 300 C.

My invention can be further understood by referring to the followingworking example in which the parts given are by Weight: 30 parts ofchlorine together with 10 parts of fresh benzene are charged to thereactor 12 in which.

the benzene is chlorinated in the presence of daylight fluorescentlights at a temperature of 50 C. The reaction products after passingthrough the scrubber, are separated in the vaporizer 16 into parts ofbenzene, which is recycled to the reactor, and 40 parts of benzene hexa-From chloride containing about 12 percent of the gamma isomer. To the 40parts of benzene hexachloride, parts of fresh methanol are addediand themixture charged to the gamma extractor maintained at a temperature ofabout C. From the filter 23, 42 parts of filter cake are charged to thecracker 35 containing ferric chloride as the catalyst. At a conversiontemperature of about 280 C. the benzene hexachloride mixture containingsome gamma but mostly non-gamma isomers is converted to 24 parts oftrichlorobenzene and 14 parts of hydrogen chloride. The conversionproducts from the cracker 35 are charged to the rectifying column 38 inwhich the top temperature is maintained at about 210 C. Twentyfour partsof trichlorobenzene of 97 percent purity are removed from the top of therectifying column. The unconverted benzene hexachloride is recycled tothe cracker. From the filter 23, 60 percent of the total gamma isomerformed in the reactor 12 together with the solvent medium are charged tothe evaporator 25 maintained at 90 C. Following crystallization andfiltering, 2 parts of gamma benzene hexachloride of 99 percent purityare removed from the filter 29. From the filter 29 and the evaporator 25are recycled 70 parts of solvent to the gamma extractor 20.

The above working example and the description of the process inconnection with the drawing are not intended to limit my invention butonly to illustrate it- I claim:

1. In a process for the production of a product containing an enhancedproportion of gamma benzene hexachloride by partially dissolving crudebenzene hexachloride obtained from the additive chlorination of benzenein a solvent selected from the group consisting of lower aliphaticalcohols, benzene, trichlorobenzene, lower alkyl acetates and loweralkyl ethers, said solvent being employed in quantities sutficient todissolve substantially all the gamma benzene hexachloride contained insaid crude benzene hexachloride, separating the thereby formed solutionfrom the undissolved solids and crystallizing a product containing anenhanced proportion of gamma benzene hexachloride from said solution,the improvement comprising recycling substantially all the solids andsolvent of the mother liquor from said crystallization step to saidpartial dissolution step.

2. The process of claim 1 in which the solvent is a lower aliphaticalcohol.

3. In a process for the production of a product containing an enhancedproportion of gamma benzene hexachloride by partially dissolving inmethanol at a temperature of about 15 to 25 C. crude benzenehexachloride obtained from the additive chlorination of benzene in thepresence of actinic light, separating the thereby formed solution fromthe undissolved solids, concentrating the solution by removal of aportion of the methanol and crystallizing a product containing anenhanced proportion of gamma benzene hexachloride from said solution,the improvement comprising recycling substantially all the solids andmethanol of the mother liquor from said crystallization step to saidpartial dissolution step.

4. The process of claim 1 wherein the selective solvent is methanol.

5. The process of claim 1 wherein the crystallization is effected byconcentrating the gamma isomer containing solution.

6. The process of claim 1 in which the partial dissolution is carriedout at a temperature between 15 25 C.

7. In a process for the production of a product containing an enhancedproportion of gamma benzene hexachloride by partially dissolving crudebenzene hexachloride obtained from the additive chlorination of benzenein a solvent selected from the group consisting of lower aliphaticalcohols, benzene,- trichlorobenzene, lower alkyl acetates and loweralkyl ethers, said solvent being employed in-quantities sufiicient todissolve substantially all the gamma benzene hexachloride contained insaid crude benzene hexachloride, separating the thereby formed solutionfrom the undissolved solids, crystallizing a product containing anenhanced proportion of gamma benzene hexachloride from said solution,and separating the crystals from themother liquor, the improvementcomprising recycling the mother liquor containing sub-- stantially allthe solids present in the mother liquor resulting from the step ofseparating the crystals.

ReferenceslCited in the file of this patent UNITED STATES PATENTS FranceJan. 10, 1953

1. IN A PROCESS FOR THE PRODUCTION OF A PRODUCT CONTAINING AN ENHANCEDPROPORTION OF GAMMA BENZENE HEXACHLORIDE BY PARTIALLY DISSOLVING CRUDEBENZENE HEXACHLORIDE OBTAINED FROM THE ADDITIVE CHLORINATION OF BENZENEIN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF LOWER ALIPHATICALCOHOLS, BENZENE, TRICHLOROBENZENE, LOWER ALKYL ACETATES AND LOWERALKYL ETHERS, SAID SOLVENT BEING EMPLOYED IN QUANTITIES SUFFICIENT TODISSOLVE SUBSTANTIALLY ALL THE GAMMA BENZENE HEXACHLORIDE CONTAINED INSAID CRUDE BENZENE HEXACHLORIDE, SEPARATING THE THEREBY